(1) Field of the Invention
The present invention is concerned with righting of boats following capsize and particularly with an inflatable device for that purpose.
(2) Desrciption of Related Art
Some boats are inherently unstable in an inverted condition and so tend to right themselves without assistance following a capsize. Others, such as sailing dinghies, can be righted by the crew while at sea. However some boats will float stably in an inverted condition following capsize and can be difficult to right. Rigid inflatable boats (“RIBs”) typically fall in this category. Clearly this poses dangers to the crew.
It is known in the art that such boats can be provided with what are referred to as self-righting devices—that is, devices which will right the boat without external intervention. An example of a vessel fitted with a self-righting device is seen in FIG. 1. This is a rigid inflatable boat (RIB) 10 of well known type, having a rigid hull 12 with inflatable tubes 14 extending along its gunwales on both sides. Boats of this general type come in a wide range of sizes and are used in many different roles. They may for example serve as military craft, as lifeboats, as tenders for larger craft etc. The example illustrated has an inboard engine but RIBs often use transom-mounted outboard engines. At the rear of the RIB 10 is a rigid arch 16 standing well above the hull and formed of metal tubing. An inflatable float 18 is mounted on a crossbar 19 at the top of the arch 16. In normal operation the float 18 is deflated and stowed in a compact configuration (not shown in the drawing) on the crossbar 19. If the RIB is overturned, by heavy seas for example, pressurised gas is supplied to the float 18 to inflate it. Clearly with the RIB 10 inverted, the float is submerged. When inflated the float 18 becomes buoyant and seeks a route to the surface. The rigid arch 16 serves as a lever through which the float 18 exerts a righting moment on the boat, causing it to roll back to an upright orientation.
The float 18 is inflated using a pressurised gas cylinder and associated valve which are not seen in the drawing.
While effective, self-righting devices of the illustrated type are not suited to all applications. In particular provision of the rigid arch 16 or some other raised, fixed structure through which the float 18 can exert the required leverage can be problematic. Where the RIB 10 is to be used as a gunboat, for example, it is important that the gun platform should have a full 360 degree view. The rigid arch 16 of FIG. 1 would potentially prevent targeting of objects behind the RIB 10, which is undesirable. Another potential problem is that a boat used as a tender may need to be stored on the parent vessel in a space with limited headroom in which the arch 16 could not be accommodated.
One might imagine that the float 18 could be replaced with a larger inflatable float mounted on the deck or transom but in practice this proves ineffective. Experience shows that a float of this type tends, in use, to pop up to the surface beside the inverted boat before it is adequately inflated, making it incapable of righting the boat.
Prior art document U.S. Pat. No. 5,056,453 (Wright) describes a rigid inflatable boat with a self-righting apparatus in the form of an inflatable arch whose ends are each anchored to a respective tube of the RIB. That is, the arch spans the entire width of the RIB. It seems to be envisaged that the arch will be formed by a single inflatable chamber to be inflated following a capsize, and that this structure will naturally tend to inflate more rapidly on one side than the other so that its asymmetric buoyancy will determine the direction in which the boat rolls. Certain drawbacks are apparent. The arch depicted in the document appears to be mounted upon and integrated with the inflatable tubes of the RIB, potentially complicating the boat's manufacture. Storage of the deflated arch, which necessarily extends right across the RIB, may also prove problematic. It is not known how effective this design would be in practice.
Hence a need exists for an improved self-righting device for a boat or other vessel. It is particularly desirable that this device should have a low profile when stowed.